Tank Type rules that shouldn't be broken (but are)

Lert: @OP, you might want to read this. You speak of tank classes and roles as if they're set-in-stone rules that some tanks break, but that's the wrong way to think about it. Class classifcations are arbitrary. How they perform is what matters. As such there are heavily armored, slow light tanks, fast and agile unarmored heavies, fast TD's with turrets, etc. Adjust to what's in front of you, not to how you believe things 'should' funtion.